The present invention generally relates to radio-frequency modules for communication, and, more particularly, to a radio-frequency module that is equipped with an antenna device and is designed for communication in microwave bands or milliwave bands, and a method of manufacturing the radio-frequency module.
In recent years, electronic apparatuses that utilize electric waves in microwave bands or milliwave bands have been increasingly produced. Particularly, electric waves in milliwave bands involving broad frequency bands that have not been used yet are suitable for high-speed, large-capacity information transmission that requires broad frequency bandwidths. Having features such as high-angle resolution and the ability to propagate in a medium that does not transmit light, such electric waves in milliwave bands are also being studied for the use in the field of sensing machines such as collision avoidance radars that are employed in vehicles or mobile robots.
Despite the high possibility of practical use, there are delays in the development and actual use of electronic apparatuses that utilize electric waves in milliwave bands, because of the high production costs of measurement instruments for millimeter electric waves and milliwave-band communication semiconductor devices that are required for the development of such electronic apparatuses.
Particularly, an MMIC (monolithic microwave IC) on which a power amplifier and a transmission/reception circuit such as an oscillator, a low-noise amplifier, and a mixer are mounted, is essential in a small-sized, light-weight milliwave-band electronic apparatus in which active elements such as a semiconductor device, passive elements such as a resistive element and a capacitor, and electric transmission lines such as microstrip lines are mounted on a single chip.
As shown in FIG. 1, in a module 100 that integrates an MMIC 101 with an antenna module 102, a hermetically sealed package 106 is often employed. In the package 106, the MMIC 101 is wire bonded or flip-chip mounted onto a ceramic substrate 104 made of alumina or the like, and a ceramic or metal cap 105 is brazed thereto. The MMIC 101 is connected to the antenna module 102 with ribbons 108 and coplanar transmission lines 109. In the antenna module 102, the MMIC 101 is connected to an antenna element 112 via waveguides 110. A transmission signal is supplied from the MMIC 101 to the antenna element 112, and is transmitted from the antenna element 112. Meanwhile, a signal received by the antenna element 112 is supplied to the MMIC 101, and signal processing or the like is performed.
However, the module 100 illustrated in FIG. 1 has the problem of high production costs. More specifically, the hermetically sealed package 106, which includes the ceramic substrate 104 and the cap 105 made of ceramics or the like, exhibits excellent reliability, but is more expensive than a resin substrate. As a result, the hermitically sealed package 106 has the problem of being not able to lower the module production costs.
Also, each of the waveguides 110 formed in the antenna module 102 is an opening that has a circular or rectangular section penetrating a ceramic board 111, and is surrounded by a conductive body. So as to form the waveguides 110 with low loss, each opening needs to be formed with high precision in terms of size. Further, as the milliwave length becomes shorter, higher accuracy is required. However, it is difficult to form a highly precise opening in the ceramic board 111, and doing so only increases the processing cost. In a case where a metal board is used instead of the ceramic board 111, the material cost for the metal board is low, but the transmission characteristics deteriorate, because a highly precise opening cannot be formed by press stamping. As a technique of forming a highly precise opening in a metal board, wire discharge processing can be performed. To do so, however, the processing cost increases, and the module production costs cannot be lowered.